US7323421B2 - Silicon wafer etching process and composition - Google Patents
Silicon wafer etching process and composition Download PDFInfo
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- US7323421B2 US7323421B2 US11/152,362 US15236205A US7323421B2 US 7323421 B2 US7323421 B2 US 7323421B2 US 15236205 A US15236205 A US 15236205A US 7323421 B2 US7323421 B2 US 7323421B2
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- hydroxide
- etching process
- chelating agent
- etching
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- 238000005530 etching Methods 0.000 title claims abstract description 90
- 229910052710 silicon Inorganic materials 0.000 title claims abstract description 61
- 239000010703 silicon Substances 0.000 title claims abstract description 61
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 60
- 238000000034 method Methods 0.000 title claims abstract description 44
- 239000000203 mixture Substances 0.000 title claims description 5
- 239000003518 caustics Substances 0.000 claims abstract description 61
- 239000002738 chelating agent Substances 0.000 claims abstract description 42
- 229910021645 metal ion Inorganic materials 0.000 claims abstract description 36
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 claims abstract description 30
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 13
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 45
- 239000012535 impurity Substances 0.000 claims description 20
- 229910052751 metal Inorganic materials 0.000 claims description 20
- 239000002184 metal Substances 0.000 claims description 20
- KCXVZYZYPLLWCC-UHFFFAOYSA-N EDTA Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O KCXVZYZYPLLWCC-UHFFFAOYSA-N 0.000 claims description 12
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 9
- -1 dimethylgloxime Chemical compound 0.000 claims description 7
- 230000000977 initiatory effect Effects 0.000 claims description 7
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 6
- DHMQDGOQFOQNFH-UHFFFAOYSA-N Glycine Chemical compound NCC(O)=O DHMQDGOQFOQNFH-UHFFFAOYSA-N 0.000 claims description 4
- AEMRFAOFKBGASW-UHFFFAOYSA-N Glycolic acid Chemical compound OCC(O)=O AEMRFAOFKBGASW-UHFFFAOYSA-N 0.000 claims description 4
- WGTYBPLFGIVFAS-UHFFFAOYSA-M tetramethylammonium hydroxide Chemical compound [OH-].C[N+](C)(C)C WGTYBPLFGIVFAS-UHFFFAOYSA-M 0.000 claims description 4
- PQHYOGIRXOKOEJ-UHFFFAOYSA-N 2-(1,2-dicarboxyethylamino)butanedioic acid Chemical compound OC(=O)CC(C(O)=O)NC(C(O)=O)CC(O)=O PQHYOGIRXOKOEJ-UHFFFAOYSA-N 0.000 claims description 2
- MFGOFGRYDNHJTA-UHFFFAOYSA-N 2-amino-1-(2-fluorophenyl)ethanol Chemical compound NCC(O)C1=CC=CC=C1F MFGOFGRYDNHJTA-UHFFFAOYSA-N 0.000 claims description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 claims description 2
- 239000004471 Glycine Substances 0.000 claims description 2
- QPCDCPDFJACHGM-UHFFFAOYSA-N N,N-bis{2-[bis(carboxymethyl)amino]ethyl}glycine Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(=O)O)CCN(CC(O)=O)CC(O)=O QPCDCPDFJACHGM-UHFFFAOYSA-N 0.000 claims description 2
- 102000004316 Oxidoreductases Human genes 0.000 claims description 2
- 108090000854 Oxidoreductases Proteins 0.000 claims description 2
- 239000000908 ammonium hydroxide Substances 0.000 claims description 2
- HUCVOHYBFXVBRW-UHFFFAOYSA-M caesium hydroxide Inorganic materials [OH-].[Cs+] HUCVOHYBFXVBRW-UHFFFAOYSA-M 0.000 claims description 2
- MGFYIUFZLHCRTH-UHFFFAOYSA-N nitrilotriacetic acid Chemical compound OC(=O)CN(CC(O)=O)CC(O)=O MGFYIUFZLHCRTH-UHFFFAOYSA-N 0.000 claims description 2
- 235000012431 wafers Nutrition 0.000 abstract description 114
- 239000007864 aqueous solution Substances 0.000 abstract 1
- 239000000243 solution Substances 0.000 description 39
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 21
- 229910052759 nickel Inorganic materials 0.000 description 9
- 238000004140 cleaning Methods 0.000 description 8
- 239000000126 substance Substances 0.000 description 8
- 230000002378 acidificating effect Effects 0.000 description 6
- 150000002739 metals Chemical class 0.000 description 6
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 description 5
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 5
- 229910001424 calcium ion Inorganic materials 0.000 description 5
- 230000007547 defect Effects 0.000 description 5
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 4
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 4
- 239000000654 additive Substances 0.000 description 4
- 229910052802 copper Inorganic materials 0.000 description 4
- 239000010949 copper Substances 0.000 description 4
- 238000005498 polishing Methods 0.000 description 4
- 230000000996 additive effect Effects 0.000 description 3
- ZQWICJYATMSSSD-UHFFFAOYSA-M chembl2028584 Chemical compound [Na+].C1=CC=C2C(N=NC3=C4C=CC=CC4=CC=C3O)=C(O)C=C(S([O-])(=O)=O)C2=C1 ZQWICJYATMSSSD-UHFFFAOYSA-M 0.000 description 3
- 238000011109 contamination Methods 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000013522 chelant Substances 0.000 description 2
- 238000003486 chemical etching Methods 0.000 description 2
- 239000000356 contaminant Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 239000003446 ligand Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Substances [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 2
- NROKBHXJSPEDAR-UHFFFAOYSA-M potassium fluoride Chemical compound [F-].[K+] NROKBHXJSPEDAR-UHFFFAOYSA-M 0.000 description 2
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- VEQPNABPJHWNSG-UHFFFAOYSA-N Nickel(2+) Chemical compound [Ni+2] VEQPNABPJHWNSG-UHFFFAOYSA-N 0.000 description 1
- BPQQTUXANYXVAA-UHFFFAOYSA-N Orthosilicate Chemical compound [O-][Si]([O-])([O-])[O-] BPQQTUXANYXVAA-UHFFFAOYSA-N 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 229910000019 calcium carbonate Inorganic materials 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 229920001429 chelating resin Polymers 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000011651 chromium Substances 0.000 description 1
- 239000008119 colloidal silica Substances 0.000 description 1
- 230000000536 complexating effect Effects 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000003203 everyday effect Effects 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910021421 monocrystalline silicon Inorganic materials 0.000 description 1
- 229910001453 nickel ion Inorganic materials 0.000 description 1
- 238000000918 plasma mass spectrometry Methods 0.000 description 1
- 229910000027 potassium carbonate Inorganic materials 0.000 description 1
- 239000011698 potassium fluoride Substances 0.000 description 1
- 235000003270 potassium fluoride Nutrition 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 239000012487 rinsing solution Substances 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 150000003376 silicon Chemical class 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 229910001428 transition metal ion Inorganic materials 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
- H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
- H01L21/30604—Chemical etching
- H01L21/30608—Anisotropic liquid etching
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K13/00—Etching, surface-brightening or pickling compositions
- C09K13/02—Etching, surface-brightening or pickling compositions containing an alkali metal hydroxide
-
- C—CHEMISTRY; METALLURGY
- C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
- C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
- C11D7/00—Compositions of detergents based essentially on non-surface-active compounds
- C11D7/22—Organic compounds
- C11D7/26—Organic compounds containing oxygen
- C11D7/265—Carboxylic acids or salts thereof
-
- C—CHEMISTRY; METALLURGY
- C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
- C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
- C11D7/00—Compositions of detergents based essentially on non-surface-active compounds
- C11D7/22—Organic compounds
- C11D7/32—Organic compounds containing nitrogen
- C11D7/3245—Aminoacids
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02002—Preparing wafers
- H01L21/02005—Preparing bulk and homogeneous wafers
- H01L21/02008—Multistep processes
- H01L21/0201—Specific process step
- H01L21/02019—Chemical etching
-
- C—CHEMISTRY; METALLURGY
- C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
- C11D—DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
- C11D2111/00—Cleaning compositions characterised by the objects to be cleaned; Cleaning compositions characterised by non-standard cleaning or washing processes
- C11D2111/10—Objects to be cleaned
- C11D2111/14—Hard surfaces
- C11D2111/22—Electronic devices, e.g. PCBs or semiconductors
Definitions
- the present invention relates, in general, to a process for etching silicon wafers with a caustic etching solution and, in particular, to a caustic etching process providing wafers having a reduced concentration of metal impurities in the wafer bulk.
- Silicon wafers are typically obtained by a multi-step process, including: slicing a single crystal silicon ingot in a direction normal to the axis of the ingot to produce thin wafers; chamfering or profiling the edges of the wafers; grinding or lapping the wafers to remove surface damage caused by the slicing process; chemically etching the wafers to remove mechanical damage produced by the prior shaping steps; and finally, chemically/mechanically polishing the edge and at least one surface of each wafer with, for example, a colloidal silica slurry and a chemical etchant to ensure that the wafers have highly flat, reflective, and damage-free surfaces.
- the wafers are then typically cleaned and quality inspected prior to being packaged. Additional cleaning steps can be introduced between these steps as required.
- silicon wafers Prior to chemical etching, silicon wafers typically exhibit surface and/or subsurface defects such as embedded particles and physical damage (e.g., micro-cracks, fractures, or stress-induced crystalline imperfections).
- the physical damage may be induced by stress applied to the wafer by processes such as lapping, grinding, and edge profiling. These defects generally occur in the region extending from the surface of the wafer to at least about 2.5 ⁇ m or greater below the surface of the wafer. To remove these defects, therefore, at least about 2.5 ⁇ m of silicon is typically removed from the surface of the wafer using an acidic and/or caustic chemical etchant, thus removing the embedded particles, contaminants, and physical damage contained in the removed layer of silicon.
- the present invention is directed to an etching process for removing silicon from the surface of a silicon wafer.
- the process comprises etching the silicon wafer with a caustic etchant in an etching apparatus to reduce the wafer's overall thickness, as measured between the wafer's two generally parallel surfaces, by at least about 5.0 ⁇ m, i.e., about 2.5 ⁇ m from both the front and back surface.
- the caustic etchant comprises water, at least about 15% by weight of a hydroxide ion source, and a metal chelating agent to sequester metal ion impurities in the caustic etchant from the surface of the silicon wafer.
- the present invention is further directed to a caustic etchant for removing silicon from the surface of a silicon wafer.
- the caustic etchant comprising water, at least about 15% by weight of a source of hydroxide ions, and chelates formed between a chelating agent and metal ion impurities in the caustic etchant.
- FIG. 1 is a graph of Ni ion concentration, comparing the bulk nickel concentration of wafers prepared according to Example 1.
- FIG. 2 is a graph of Ni ion concentration, comparing the nickel out-diffusion concentration of wafers prepared according to Example 2.
- metal contamination of silicon wafers may be reduced during a caustic etching process by including a metal chelating agent in the etchant.
- the metal chelating agent advantageously sequesters copper, nickel, chromium, iron, and other such metals that may contaminate the etched wafer.
- the chelating agent is especially effective at sequestering copper and nickel, which could otherwise potentially diffuse into the bulk of the silicon wafer during the etching process.
- a caustic etchant of the present invention thus comprises one or more hydroxide ion source(s) such as sodium hydroxide, potassium hydroxide, lithium hydroxide, cesium hydroxide, ammonium hydroxide, or tetramethylammonium hydroxide.
- the caustic etchant comprises potassium hydroxide.
- the etchant comprises at least 15% by weight of a hydroxide ion source(s). More typically, the etchant will comprise at least 40 wt %, still more typically at least about 45 wt %, and still more typically at least about 65 wt % of the hydroxide ion source(s).
- the concentration of the hydroxide ion source is preferably near the saturation point.
- the concentration be maintained at a value less than the saturation value (at the etching temperature).
- concentration of the hydroxide ion source be at least 70% but no more than 95% of the saturation concentration of the source of hydroxide ions. More preferably, the concentration of the hydroxide ion source is at least about 74% but no more than 95% of the saturation concentration. Still more preferably, at least about 77% but no more than 95% of the saturation concentration.
- any chelating agent capable of complexing metal ions such as copper and nickel, may be used in the etchant.
- the chelating agent is a composition capable of forming several coordinate bonds with a single metal ion, such that the resulting chelates are relatively stable in the etching solution and may comprise one or more multidentate ligands (e.g., bidentate, tridentate, and hexadentate ligands).
- Preferred chelating agents include, for example, ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentacetic acid, glycolic acid (available as GLOXYME from Bayer Chemical), glycine (oxidase) (available from Bayer Chemical), dimethylgloxime, nitrilotriacetic acid, and iminodisuccinic acid (available as BAYPURE from Bayer Chemical).
- the chelating agent is EDTA.
- EDTA is versatile in that it can form up to six bonds with a metal ion and is able to readily form chelates or complexes with both transition-metal ions and main-group metal ions.
- the etchant be formed by combining sufficient chelating agent with the hydroxide ion source and water to reduce the free metal ion concentration in the etchant to a value of less than about 1 ppb. More preferably, the free metal ion concentration in the fresh etchant, i.e., before it is brought into contact with a silicon wafer is less than about 0.5 ppb. Even more preferably, the free metal ion concentration in the fresh etchant is less than about 0.05 ppb.
- the remainder of the free metal ions originally carried by the hydroxide ion source (or even the water used to form the etchant) will be present in the etchant as a metal chelate and thus have substantially less potential to contaminate the silicon wafer during the etching process.
- Hydroxide ion sources are not the only sources of metal ions during silicon wafer etching processes.
- Other sources include, for example, the etching apparatus (e.g., the tank, pump, thermocouple, wafer cassettes, or other components of or used in the etching apparatus) and even the surfaces of the silicon wafers themselves.
- the etchant at least initially, contain free chelating agent. That is, it is generally preferred that the etchant contain more chelating agent than is required to complex the metal ion impurities introduced solely by the hydroxide source.
- the concentration of free chelating agent in the caustic etchant is preferably at least about 100 ppm, more preferably at least about 200 ppm, even more preferably at least about 350 ppm, and still more preferably at least about 500 ppm.
- the molar ratio of chelating agent added to the etching solution relative to the concentration of metal ion impurities introduced from the source of hydroxide ions is preferably at least about 5:1, more preferably, at least about 10:1, and still more preferably at least about 100:1.
- the caustic etchant may additionally comprise a range of additives.
- the etchant may comprise a salt additive such as potassium fluoride or potassium carbonate, which contributes to improved surface characteristics; see, e.g., PCT application No. WO 2004/027840 A2, published Apr. 1, 2004.
- the caustic etchant may be prepared in the etching apparatus itself (prior to the introduction of the wafers) or the etchant can be preformed by combining the components thereof before introduction to the etching apparatus.
- silicon wafers are typically etched by being immersed in a tank holding a volume of the etchant.
- the components of the caustic etchant may be combined in the etchant tank before the wafers are introduced, or the components may be combined outside the tank, and the resulting mixture is then introduced to the tank.
- the silicon wafers and caustic etchant (lacking a chelating agent) may alternatively be combined in the etching tank before the chelating agent is introduced.
- Silicon wafers to be etched in accordance with the process of the present invention may be prepared by any means generally known in the art. Typically, these wafers contain surface and/or subsurface defects as a result of certain previous processing steps with the defects extending from the surface of the wafer to a depth of at least about 2.5 ⁇ m from the surface of the wafer.
- the silicon wafer is introduced to an etching apparatus where the wafer is contacted with the caustic etchant. Contact may occur by spraying the etchant onto the wafer, spin etching, or, more preferably, by immersing the silicon wafer(s) (individually or simultaneously in a carrier) in a body of etchant. Suitable immersion etchers include those commercially available from SPEC (Valencia, Calif.), Toho (Japan), and Dan Science (Japan).
- the caustic etchant is typically maintained at a temperature of about 70° C. to 120° C. Within this range, the temperature will more typically be at least about 75° C. and, still more typically, at least about 80° C. For example, in one embodiment, the temperature of the etchant is typically maintained between about 75° C. and about 90° C., or even about 75° C. to about 85° C.
- the caustic etching solution comprises a salt additive as described above
- higher temperatures within the ranges set forth above e.g., temperatures from about 100° C. to about 120° C.
- the wafer is etched until the desired amount of material removal is achieved.
- the wafer is etched to remove a layer of silicon from the wafer's surface having a thickness of at least about 2.5 ⁇ m. This reduces the wafer's overall thickness by at least about 5.0 ⁇ m as measured between the wafer's two generally parallel surfaces. More typically, the wafer is etched to remove a layer of silicon from the wafer's surface having a thickness of at least about 5.0 ⁇ m.
- etching may proceed for a time sufficient to remove a layer of silicon from the wafer's surface having a thickness of between about 5.0 ⁇ m to about 15 ⁇ m, more typically from about 7.5 ⁇ m to about 12.5 ⁇ m, and still more typically from about 8.5 ⁇ m to about 11.5 ⁇ m.
- the wafer will typically be contacted with the etchant for at least 5 minutes.
- the surface of the wafer remains in contact with the caustic etchant for about 5 minutes to about 15 minutes, preferably for about 9 minutes to about 11 minutes, and, more preferably, for about 10 minutes to about 10.5 minutes.
- a volume of etchant is used, or reused, to etch a series of silicon wafers or cassettes of silicon wafers until the silicate concentration in the etchant becomes undesirably high.
- the etchant may periodically receive additional amounts of water, hydroxide ion source, chelating agent, or other components of the etchant to replace any such depleted component which evaporates, is consumed by the etching process, is carried out of the etching apparatus by the wafers or carriers for the wafers, or is otherwise removed.
- additional chelating agent may be added to the etching tank as necessary to sequester metal ion impurities generated in situ or carried in by the etchant so that the concentration of free metal ion impurities in the caustic etching solution contacting the silicon wafer(s) is maintained at a value of less than about 100 ppb by weight, more preferably less than about 50 ppb by weight, and even more preferably less than about 25 ppb by weight.
- the concentration of free chelating agent or metal ion concentration in the etchant may be monitored by means commonly known in the art.
- free chelating agent concentration is monitored by titrating an amount of the caustic etching solution from the etching tank and introducing it to a fixed amount of calcium carbonate that contains calcium ions in excess of the amount that could be complexed by the maximum concentration of chelating agent.
- An indicator can be used to measure the amount of calcium ions originally present.
- One such indicator is calcon or solochrome dark blue (eriochrome blue black R, sodium 1-(2-hydroxy-1-naphthylazo)-2-naphthol-4-sulphonate).
- the free chelating agent from the etching solution complexes some amount of calcium ions.
- the indicator is used to measure the calcium ion level, thereby giving the total amount of calcium ions that were complexed by the chelating agent of the etching solution, which is then used to determine the amount of chelating agent present in the etching solution. If the level of chelating agent is insufficient, additional chelating agent can be introduced to return the concentration thereof to an appropriate level. Further, the measurement of the concentration can take place at a regular interval, ensuring adequate chelating agent concentration is maintained throughout the etching process. In one embodiment, the concentration of chelating agent is monitored about once every day.
- a wafer etched in accordance with the present invention is typically removed from the etchant and cleaned before subsequent processing. After etching, the wafer is typically subjected to several processing steps involving polishing and cleaning to prepare the surface to a condition acceptable for semiconductor device manufacturers.
- a caustic etching solution was formed by combining water and KOH in ratios to form 45 wt % KOH solution.
- a typical etching bath quantity of 120 liters of this solution was formed.
- the KOH source was electronic grade, reporting a maximum impurity level of 1 ppm by weight of metal impurities. For 120 liters of solution, this corresponds to 0.003 moles of metal ion impurities.
- Twenty-five (25) wafers were immersed in the caustic etching solution. The wafers were an assortment of P ⁇ , P+, and P++ doped wafers.
- the silicon wafers were contacted with the caustic etching solution for 10 minutes while the solution was maintained at 80° C., removing about 20 ⁇ m of total stock from the front and back of the wafers.
- the etching solution was modified according to this invention by adding 0.2 moles of EDTA (approximately 65 g) directly to the caustic etchant. This amount equates to over sixty-six times the amount of EDTA needed to chelate the 0.003 moles of metal ions from the KOH source. Twenty five (25) silicon wafers of assorted doping were then introduced to this caustic etching solution in the etching tank. The silicon wafers were contacted with the caustic etching solution for 10 minutes while the solution was maintained at 80° C., removing about 20 ⁇ m of total stock from the front and back of the wafers.
- EDTA approximately 65 g
- the wafers were thoroughly rinsed with a rinsing solution comprising approximately 0.1 M hydrochloric acid to remove any surface metals from the wafers. Subsequent cleaning in SC1 followed by a hydrofluoric cleaning solution further reduced surface metal values to a level of approximately 1 ⁇ 10 10 /cm 2 or lower. Next, the wafers were heat treated at 350° C. for 3 hours to bring nickel atoms from the interior to the wafer to the wafer's surface. The wafers were then treated with a solution of hydrofluoric acid and hydrogen peroxide to extract surface metals from the wafers.
- This extraction solution was prepared by combining 10 mL of 49% HF and 20 mL of 31% H 2 O 2 with 70 mL of deionized water.
- the extracted substance was analyzed using Inductively Couples Plasma Mass Spectrometry (ICPMS) to determine the metal concentration therein.
- ICPMS Inductively Couples Plasma Mass Spectrometry
- silicon wafers were fully processed using a caustic etching solution.
- Four (4) of these wafers were processed using a standard, untreated etching solution as detailed in Example 1, while four (4) were processed using a modified etching solution according to the modified caustic etchant detailed in Example 1.
- four (4) silicon wafers were fully processed using an acidic etching solution.
- Each of these groups had two (2) P ⁇ wafers and two (2) P++ wafers.
- a “fully processed” wafer is one that has been subjected to grinding or lapping, chemical etching, chemical/mechanical polishing, and polished wafer cleaning.
- the first group of silicon wafers to be etched with a standard, unmodified caustic etchant were contacted with the KOH solution described in Example 1 for 10 minutes while the solution was maintained at 80° C., removing about 20 ⁇ m of total stock from the front and back of the wafers.
- the second group of silicon wafers to be etched with a chelating agent-modified caustic etchant were contacted with the EDTA-modified KOH solution described in Example 1 for 10 minutes while the solution was maintained at 80° C., removing about 20 ⁇ m of total stock from the front and back of the wafers.
- the wafers were subjected to standard polishing and cleaning procedures. For the cleaning procedures, all the wafers were thoroughly rinsed through SC1 and SC2-type cleaning processes to remove any surface metals from the wafers. Next, the wafers were heat treated at 350° C. for 3 hours to outdiffuse nickel ions. The wafers were then treated with a solution of hydrofluoric acid and hydrogen peroxide as disclosed in Example 1 to extract surface metals from the wafers. The extracted substance was analyzed using ICPMS to determine the metal concentration therein. The results of this analysis is shown in FIG. 2 .
- the wafers that were etched with the EDTA-modified caustic etchant had nickel values in both the P++ wafers and P ⁇ wafers similar to the P++ wafers and P ⁇ wafers etched with the acidic etching solution (AE(std.)), and with nickel values in the P++ wafers well below those etched in the unmodified caustic etching solution (CE(KOH)).
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US20080099717A1 (en) | 2008-05-01 |
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US7938982B2 (en) | 2011-05-10 |
TW200616072A (en) | 2006-05-16 |
US20060011588A1 (en) | 2006-01-19 |
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